Oceans cover some 70% of the earth's surface. These bodies of water contain vast reservoir of energy mainly due to solar heating and wind stresses. If this energy can be harnessed, a large portion of the worlds energy needs may be met in clean and renewable manner. Various devices have been developed to utilize this energy, including, ocean thermal energy conversion devices (OTEC), tidal power devices, wave power generators and flowing water (current) turbines.
OTEC devices have been proposed since the late 1800's. The OTEC devices generate electricity using the temperature difference of seawater at different depths that result from solar heating by the sun. An extreme example of this thermal differential can be seen in the arctic regions where a 40° C. temperature difference exists between the local air and the water temperature during the winter. Even in tropical and subtropical regions, as much as a 20° C. temperature differential may exist. Through a type of heat engine such as an Anderson cycle engine, the temperature differences between the surface and the ocean depths are utilized to heat and cool a working fluid. The heated working fluid is expanded through a turbine to generate electrical power. The heat is dissipated from the working fluid by the colder ocean depths and compressed before being returned to the surface to be reheated.
Another device utilizes tidal power as a means of electricity generation that is achieved by the capturing of energy contained in moving water mass due to tides. The source of the tidal energy comes from the slow deceleration of the Earth's rotation caused by the moon. Two types of tidal energy can be extracted: kinetic energy of currents between ebbing and surging tides and potential energy from the difference in height between high and low tides. The extraction of potential energy typically involves building a barrage and creating a tidal lagoon. The barrage traps a water level inside a basin. Pressure or “head” is created when the water level outside of the basin or lagoon changes relative to the water level inside. The head is used to drive turbines. This design leads to a decrease in the tidal range inside the basin or lagoon, resulting in a reduced transfer of water between the basin and the sea. This reduced transfer of water accounts for the energy produced by the scheme. The efficiency of tidal power generation in ocean dams largely depends on the amplitude of the tidal swell, which can be up to 10 meters where the periodic tidal waves funnel into rivers and fjords. Amplitudes of up to 17 meters occur in areas such as the Bay of Fundy in Canada, where tidal resonance amplifies the tidal waves.
Wave power devices produce energy, as the name suggests, through the movement of ocean surface waves. Wave size is determined by wind speed and the distance over which the wind excites the waves. Other factors affecting wave size include the depth and topography of the seafloor which can focus or disperse the energy of the waves. For a given wind speed there is a limit over which time or distance will not produce larger waves. The potential energy of a set of waves is proportional to wave height squared times the “period” or the time between wave crests. Longer period waves have relatively longer wavelengths and move faster. The wave power device typically includes some type of buoy that is connected to some type of actuator the converts the up and down motion of the waves into a form of usable power that drives the electrical generator directly or store the energy in another form (e.g. hydraulic or compressed air) for later use.
The most promising of the technologies used to tap the ocean's energy uses techniques similar to wind turbines. Flowing water or current turbines extract kinetic energy from the flow of water similar to the way wind turbines do with air. However, water currents, unlike air currents, tend to be highly predictable and consistent over time making water turbines a highly attractive source of power. Generally, the system includes a rotor capable of interacting with the flow of water such that the passing water produces a force on the rotor blades creating a rotational movement. A number of water turbines have been proposed to overcome the problems associated with deploying a submerged power system. Typically, the water turbine is transported to the desired location on a barge and supported in position using either a structure embedded in the floor or through a surface floating system that is anchored in position. The logistics involved in transporting, installing and servicing prior water turbines is substantial.
While existing water turbine power systems are suitable for their intended purposes, there still remains a need for improvements in providing a system that may be readily deployed, installed and serviced with a minimum amount of ancillary support vessels. In particular there is a need for a self contained water turbine power system that may be deployed using a simple towing vessel.